Chapter 12 The Reproductive System & Genetics

Reproduction means being able to produce new individuals (babies)Two methods

1. Asexual Reproduction: - one parent only and the offspring are clones of the parent.

2. Sexual Reproduction: - two parents a male and a female - offspring are not clones of parent.

Gametes (Sex Cells)

• Gametes (sex cells) are needed for sexual reproduction

• Each parent produces a sex cell or gamete

• male gamete = sperm

• female gamete = egg

Fertilisation

Fertilisation is the fusion between the male and female gametes to produce a zygote

• Male gonads are called testes and they are held in the scrotum.

• This means they are kept at slightly lower than body temperature (35°) which is the ideal temperature for sperm production.

A gonad is an organ that produces sex cell in animals.

Role of the Male Reproductive System1. To produce sperm2. To deliver sperm into the female body.

Urethra

• The urethra carries semen and urine out of the body

Facts about sperm•The volume of semen in a single ejaculation may vary from 1.5 to 6.0 ml.

•There are usually between 50 to 150 million sperm per millilitre of semen

Summary of functions of main parts of male reproductive system

Part Function

Testis Produces sperm and testosterone

Sperm duct Carries sperm from the epididymis to the urethra

Seminal vesicles, Cowper’s gland and

Prostate gland

Produces seminal fluid which feeds the sperm and allows them to swim. Sperm and seminal fluid are

collectively called semen.

Urethra Allows the passage of either urine or sperm.

Penis Places sperm inside the body of a female

ScrotumKeeps testes at a lower temperature (35°). This is the

optimum temperature for Meiosis to occur.

Male Hormone - Testosterone• Testosterone is the hormone responsible for

Development of male sex organs1. Sperm production

2. development of the secondary male sexual characteristics

The growth of pubic, facial and body hair

• The enlargement of larynx and ‘breaking’ of the voice

• Increased muscular and bone

• A growth spurt at puberty

• An increased secretion of sebum in the skin

Male Secondary Sexual characteristicsSecondary sexual characteristics refer to features that distinguish males from females, apart from the sex organs themselves

Structure of the female reproductive system

The Uterus (womb)

• Inner lining of the womb is called the endometrium

• This lining thickens each month with cells and blood vessels to nourish the embryo.

•

Summary of functions of main parts of female reproductive system

Part Function

OvaryTo produce the egg (ova). To produce the hormones

oestrogen and progesterone

Fallopian tube

(oviduct) Catches the egg from the ovary and transports it to

uterus. Site of fertilisation.

Uterus

Site of implantation. Holds the developing embryo. Has a lining (endometrium) enriched with blood

vessels to nourish the embryo.

Forms the placenta.

Vagina Allows entry of sperm and exit of baby at birth.

Female Hormones

• A combination of oestrogen and progesterone hormones at puberty causes the development of the secondary female sex characteristics:

• The maturing and enlargement of the breasts.

• The widening of the pelvis to allow for birth.

• The growth of pubic and underarm hair.• A growth spurt.

Puberty is the time when the sex organs mature and other physical and emotional changes take place.

Puberty in Boys

Begins about 13-15 years old.

Sexual features develop during puberty including:

The shoulders broaden, voice breaks, increase in body muscle etc.

Puberty in Girls

Begins around the age of 12-13 years

Sexual features that develop during puberty include:

Breasts enlarge, ovaries and womb grow in size etc.

Events in the menstrual cycleDays 1 – 5

1. Menstruation (period). The old lining of the uterus breaks down and leaves the body.

2. A new egg is produced in the ovary.Days 6 - 14

1. The lining of the uterus builds up again in preparation for implantation.

2. Oestrogen also prevents the development of any more eggs.

Day 14

1. Ovulation. The release the egg into the fallopian tube.

Days 14 - 28

1. The uterus lining thicken even further.

If fertilisation does not take place:

The egg that was released will die by day 16 if it is not fertilised. The lining of the uterus breaks down again on day 28.

The menstrual cycle begins again with day 1.